"""Persona: Lyra's identity and voice, loaded from an editable markdown prompt.

The prompt lives in `personas/<name>.md` so it can be tuned without touching
code. `LYRA_PERSONA` selects which file to load (default: "lyra").
"""
from __future__ import annotations

import os
from functools import lru_cache
from pathlib import Path

_PERSONA_DIR = Path(__file__).parent / "personas"


@lru_cache(maxsize=None)
def system_prompt(name: str | None = None) -> str:
    """Return the persona system prompt. Cached; pass a name to override env."""
    name = name or os.getenv("LYRA_PERSONA", "lyra")
    path = _PERSONA_DIR / f"{name}.md"
    return path.read_text(encoding="utf-8").strip()